Diffusers are conventionally used to support aerobic biological processes in aerated wastewater treatment systems. A diffuser typically comprises a disc-, tube-, or strip-shaped membrane that is constructed of rubber or other similar materials and which is punctured to provide a number of perforations in the form of holes or slits. In operation, pressurized air is sent through these perforations to create a plume of small bubbles. The bubbles rise through the wastewater and, in so doing, provide the surrounding wastewater with the oxygen needed to sustain the desired biological processes occurring therein. The rising bubbles also provide a mixing function.
FIG. 1 shows a partially cutaway perspective view of a fine bubble diffuser 100 that might be used in a wastewater treatment facility. Wastewater treatment with such diffusers is described in, as just one example, F. L. Burton, Wastewater Engineering, McGraw-Hill College, 2002, which is hereby incorporated by reference herein. In the diffuser 100, a flexible diffuser membrane 110 sits atop a diffuser body 120. The diffuser body comprises a threaded connector 130, an air inlet pipe 140, an orifice 150, and a receiving surface 160 for coupling to a retainer ring 170. The retainer ring 170 holds the flexible diffuser membrane 110 against the diffuser body 120. When gas is applied to the flexible diffuser membrane 110 through the air inlet pipe 140 and the orifice 150, the gas pressure expands the membrane 110 away from the diffuser body 120 and causes the membrane's perforations to open so that the gas discharges through them in the form of fine bubbles. When the gas pressure is relieved, the flexible diffuser membrane 110 collapses on the diffuser body 120 to close the perforations and prevent the liquid from entering the diffuser body 120 in the opposite direction. Generally, a flexible diffuser membrane configured in this way produces bubbles smaller than five millimeters in diameter. The resultant large ratio of surface area to volume in these bubbles promotes efficient oxygen mass transfer between the bubbles and the wastewater.
In use, the above-described diffusers are typically supplied with pressurized air by a network of piping that covers most of the floor of a wastewater treatment tank. In addition to the diffusers, the network of piping may also include ancillary equipment such as moisture purge systems and differential pressure monitoring systems. Nevertheless, a wastewater treatment tank is a harsh and dynamic environment, and piping and diffusers periodically fail as a result. Extreme temperature deviations and the resultant thermal expansion/contraction of thermoplastic parts, as well as unwanted vibrations (e.g., air hammering), may, for example, cause a pipe sidewall, joint, end cap, or support anchor to fail. At the same time, leaks may form in the piping, resulting in undesirable water or sludge buildup inside the network that can drastically affect system efficiency.
While these several failure modes exist in almost every aerated wastewater treatment system, there is a general lack of effective ways of monitoring these systems and detecting small problems early before they turn into catastrophic failures. The typical method of monitoring the health of an installed aeration system consists of looking for: 1) changes in surface bubble and water flow patterns; 2) the existence of water or sludge in a moisture purge line that connects to the network of piping under the surface; 3) an increase in the air pressure required to maintain a given rate of air transport through the network of diffusers; 4) a change in dissolved oxygen in one or more zones of a tank as measured by dissolved oxygen probes; 5) a change in effluent quality as measured by parameters such as biochemical oxygen demand concentration or ammonia concentration; and 6) an increase in air volume required to maintain a steady dissolved oxygen concentration in the wastewater. Nevertheless, these are all macro indicators. In other words, they may indicate serious problems such as diffuser membrane fouling, water or sludge in the pipes, or an aeration system that is otherwise compromised, but, at that point, the problem is already causing disruption to the system performance either in a failure to provide efficient treatment or a failure to provide high quality effluent.
For the foregoing reasons, there is a need for systems and methods for effectively providing early detection of defects in aerated wastewater treatment systems and other systems that utilize submerged pipes for the transport of gases before those defects become more serious failures and result in system disruption.